I know that a lot of people have suggested dyslexia, but I wondered if you've experienced some trauma? I'm a therapist and have spoken with people in the past who struggle to take in what they are reading because their head won't allow it. I wondered if that rings true for you? Only because you said you used to be fine.

If I'm wrong, I heartily apologise, maybe this isn't the ideal suggestion for a public forum about books.

You're not the problem here though, well done for being brave enough to ask. I'd definitely start with light books, in the morning in a well lit room, with a notepad alongside you to jot down points. I get this way when reading academic literature and these things definitely help me.